## Location On Earth

The more you understand about stars and their motions, the more you will enjoy stargazing. A celestial globe helps you locate sky objects as a terrestrial (Earth) globe helps you locate places on Earth.

Remember how Earth maps work. We picture the Earth as a sphere and draw imaginary guidelines on it. All distances and locations are measured from two main reference lines, each marked 0°. One line, the equator, is the great circle halfway between the North and South Poles that divides the globe into halves. The other line, the prime meridian, runs from pole to pole through Greenwich, England.

Imaginary lines parallel to the equator are called latitude lines. Those from pole to pole are called longitude lines, or meridians. You can locate any city on Earth if you know its coordinates of latitude and longitude. Distance on the terrestrial sphere can be measured by dividing the sphere into 360 sections, called degrees (°). (Angular measure is defined in Appendix 3.)

Refer to the globe in Figure 1.4. Identify the equator; prime meridian; 30°N latitude line; and 30°E longitude line. (a)_________; (b)_________; (c)

Answer: (a) 30°N; (b) 30°E; (c) equator; (d) prime meridian.

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Figure 1.4. Terrestrial globe.